1. Field of the Invention
The invention relates to the application, drying and curing of coatings on continuous filaments and more particularly relates to improved apparatus and methods for doing so.
2. Brief Description of the Prior Art
Coatings on continuous filaments to alter or improve the physical and chemical properties of the uncoated filament are commonly utilized in industry. A typical process for coating continuous filaments might consist of a large open tank with submerged driven rolls to advance the filaments through the coating solution. Such a system may suffer many disadvantages, for example, large volumes of coating solution are necessary to completely submerge the driven rolls; uniform temperature control of the coating solution may be difficult to maintain; and reactive coating solutions may require larger make-up flows or frequent replacement. Also, operation at elevated temperatures may cause problems with hazardous vapor control and undesirable film formation at the bath surface. Additional problems may occur if the coating solution is corrosive in nature and attacks some of the mechanical components of the submerged drive rolls such as bearings and seals. These deficiencies, among others, of conventional coating apparatus and processes are a disadvantage to the efficient, controlled, continuous coating of monofilament or multi-filament substrates.
The drying and curing of coatings applied to the surfaces of filaments also raises technical difficulties. For example, controlling the temperature, the uniform and complete removal of solvent and the uniform curing of the coating can be difficult and complex.
This invention presents new apparatus and a method for efficient and controlled application of a coating solution onto continuous filaments, and for controlling the environment surrounding the coated filament as the coating dries and cures. The apparatus and the method of the invention are particularly useful for coating continuous hollow fiber filaments to be employed as separating membranes. The hollow fiber substrates, preliminary to coating, are generally saturated with water, solvent materials, non-solvent liquids and like materials which may interfere with or complicate the application, drying and curing of special coatings required to form a composite separatory membrane of the hollow fiber filaments. In the method of the invention, the inherently present fluids are removed and replaced with specific coatings on the filament surfaces.